The present invention relates to amplifiers and to circuits including such amplifiers.
Modern integrated circuit differential amplifiers exhibit very high input impedence and very low drift with variation in temperature. Buffer amplifiers are conventionally formed from a differential amplifier configured as a voltage follower in which the output of a differential amplifier is connected to the inverting input and an input signal is applied to the non-inverting input.
However, with integrated circuit differential amplifiers, because of inherent inter-track capacitance imposed by the physical makeup of the circuit, the differential amplifier will have an input capacitance, typically 1.5 pF. This input capacitance is due, in the main, to capacitive coupling between the non-inverting input and the positive and negative supply lines.
This input capacitance does not normally present any problem when the amplifier is used in conventional applications. However for very specialised designs, e.g. precision capacitance measuring systems this small input capacitance will cause unacceptable non-linearities, therefore an amplifier with zero input capacitance is desirable.
The present invention provides an amplifier with effectively zero input capacitance.